1. Field of the Invention
The present invention relates to semiconductor devices, and more particularly to a semiconductor device with a signal transfer line.
2. Description of the Background Art
FIG. 11 is a block diagram showing a main part of a conventional semiconductor integrated circuit device.
Referring to FIG. 11, the semiconductor integrated circuit device includes a bus 30, a transmission side circuit 31 connected to one end of bus 30, and a reception side circuit 32 connected to the other end of bus 30. Bus 30 includes N (N is an integer of at least 2) bus lines L1-LN.
Signals VO1-VON output from transmission side circuit 31 are transferred to reception side circuit 32 via bus lines L1-LN, respectively. Reception side circuit 32 responds to signals VO1-VON to carry out a predetermined operation.
FIG. 12 shows the semiconductor integrated circuit device of FIG. 11 in more detail. In FIG. 12, only the four adjacent bus lines Lnxe2x88x921xcx9cLn+2 out of the N bus lines L1-LN and components corresponding thereto are depicted.
Referring to FIG. 12, four drivers 33 are provided corresponding to four bus lines Lnxe2x88x921xcx9cLn+2, respectively, at reception side circuit 31. The four drivers 33 are rendered active in response to a driver control signal/E attaining an activation level of xe2x80x9cLxe2x80x9d to provide signals VOnxe2x88x921xcx9cVOn+2 having levels identical to those of internal signals VInxe2x88x921xcx9cVIn+2 to one ends of bus lines Lnxe2x88x921xcx9cLn+2.
Each of bus lines Lnxe2x88x921xcx9cLn+2 has a line resistance R and a inter-line capacitance C of values determined by the line length, line width, and the like. Signals VOnxe2x88x921xcx9cVOn+2 applied to one ends of bus lines Lnxe2x88x921xcx9cLn+2 are transmitted to the other ends of bus lines Lnxe2x88x921xcx9cLn+2.
Four receivers 34 are provided corresponding to four bus lines Lnxe2x88x921xcx9cLn+2 at reception side circuit 32. The four receivers 34 detect whether the potentials at the other ends of bus lines Lnxe2x88x921xcx9cLn+2 are higher or lower than the reference potential, and reproduces signals VInxe2x88x921xcx9cVIn+2 according to the detected result. Reception side circuit 32 carries out a predetermined operation according to the reproduced signals VInxe2x88x921xcx9cVIn+2.
In such a semiconductor integrated circuit device, the occupation ratio of inter-line capacitance C as to the capacitance of the wiring is increasing according to the microminiaturization of the process. For example, in the 0.15 xcexcm process, inter-line capacitance C corresponds to 90% of the capacitance of the wiling, whereas the remaining 10% corresponds to the line-substrate capacitance, fringe capacitance, and the like. In a semiconductor integrated circuit device, coupling noise by interline capacitance C has become problematic.
For example, when signal VIn is driven from an L level to an H level or from an H level to an L level under the state where signal VIn+1 is held at an H level or an L level in FIG. 12, the level of signal VOn+1 will be altered by the coupling noise.
More specifically, in the case where signal VIn is driven from an L level to an H level when signal VOn+1 is at an H level as shown in FIG. 13, signal VOn+1 rises in a pulsive manner (this noise is referred to as xe2x80x9ccoupling noise 1xe2x80x9d hereinafter). In the case where signal VIn is driven to an L level from an H level when signal VOn+1 is at an L level, signal VOn+1 is reduced in a pulsive manner (this noise is referred to as xe2x80x9ccoupling noise 2xe2x80x9d).
In the case where signal VIn is pulled down to an L level from an H level when signal VOn+1 is at an H level, signal VOn+1 is reduced in a pulsive manner (this noise is referred to as xe2x80x9ccoupling noise 3xe2x80x9d hereinafter). In the case where signal VIn is pulled up to an H level from an L level when signal VOn+1 is at an L level, signal VOn+1 rises in a pulsive manner (this noise is referred to as xe2x80x9ccoupling noise 4xe2x80x9d hereinafter).
Coupling noises 1 and 2 among the above-described noises will delay the level change of signal VOn+1 when signal VOn+1 is altered in opposite phase to signal VOn, whereby the operating speed of the semiconductor integrated circuit is reduced. Also, coupling noises 3 and 4 cause receiver 34 to operate erroneously when signal VOn+1 attains a large noise that exceeds the reference potential of receiver 34.
These problems have been dealt by setting the line intervals of bus lines L1-LN as wide as possible. However, bus lines L1-LN cannot enjoy the advantages of process microminiaturization with this measure. In microprocessors, memories, and the like, the amount of data to be processed at one time is increasing from 32 bits to 64 bits, and further to 128 bits corresponding to the requirement of high speed processing. As a result, the number N of bus lines L1-LN is also increasing. Therefore, increasing the interval of bus lines L1-LN is not preferable since the layout area will be increased.
In view of the foregoing, a main object of the present invention is to provide a semiconductor device of small layout area and low noise level.
According to an aspect of the present invention, a semiconductor device includes a driver having an output node connected to one end of a signal transfer line, driving the output node to a first potential in response to a first signal and to a second potential differing from the first potential in response to a second signal, and a noise limiter with a first diode element having a first electrode receiving a third potential corresponding to the first potential shifted in level towards the second potential side by a threshold voltage, and a second electrode connected to the signal transfer line, and rendered conductive in response to the potential of the signal transfer line exceeding the first potential. When coupling noise 1 or 2 is generated at the signal transfer line so that the potential of the signal transfer line exceeds the first potential, the first diode is rendered conductive to restore the potential of the signal transfer line to the first potential. Therefore, the level of coupling noise 1 or 2 can be reduced. Also, only a small layout area is required since the interval of the signal transfer lines does not have to be increased.
Preferably, the noise limiter includes a second diode element having a first electrode receiving a fourth potential corresponding to the second potential shifted in level towards the first potential side by a threshold voltage, and a second electrode connected to the signal transfer line, rendered conductive in response to the potential of the signal transfer line exceeding the second potential. When coupling noise 2 or 1 is generated at the signal transfer line so that the potential of the signal transfer line exceeds the second potential, the second diode element is rendered conductive to restore the potential of the signal transfer line to the second potential. Therefore, coupling noise 2 or 1 can be reduced.
The semiconductor device preferably includes a receiver having an input node connected to the other end of the signal transfer line to receive first and second signals by detecting the potential of the input node. The noise limiter is connected to the signal transfer line at a connection node closer to the input node of the receiver than the output node of the driver. Since coupling noises 1 and 2 become larger as approaching the receiver, coupling noises 1 and 2 can be reduced effectively by connecting the noise limiter with the signal transmission line at an output point closer to the input node of the receiver than the output node of the driver.
The noise limiter is preferably provided in the proximity of the input node of the receiver. Since coupling noises 1 and 2 attain the maximum level in the proximity of the receiver, coupling noises 1 and 2 can be reduced effectively by providing the noise limiter in the proximity of the input node of the receiver.
The signal transfer line is preferably divided into a plurality of sub signal transfer lines. The semiconductor device further includes a signal transfer circuit provided between each of the plurality of sub signal transfer lines, having an input node connected to a sub signal transfer line located at an upstream side and an output node connected to a sub signal transfer line located at a downstream side to output a potential of a level identical to that of the input potential. The noise limiter is provided corresponding to each signal transfer circuit, and located in the proximity of the input node of a corresponding signal transfer circuit. In this case, coupling noises 1 and 2 can be reduced effectively even if the length of the signal transfer line is great.
Preferably, the signal transfer line is provided in plurality parallel to each other. The driver and noise limiter are provided corresponding to each signal transfer line. The semiconductor device further includes a delay circuit provided corresponding to one signal transfer line of every two adjacent signal transfer lines, connected between the output node of a corresponding driver and one end of a corresponding signal transfer line to delay the potential change by a predetermined time. In this case, the drive timing of two adjacent signal transfer lines can be shifted to reduce the influence of coupling noises 1 and 2.
Preferably, the signal transfer line is provided in plurality parallel to each other. The driver and noise limiter are provided corresponding to each signal transfer line. The semiconductor device further includes a control circuit to render active a driver corresponding to one signal transfer line out of each adjacent two signal transfer lines, and then rendering a driver corresponding to the other signal transfer line at an elapse of a predetermined time. In this case, the drive timing of two adjacent signal transfer lines can be shifted to reduce the influence of coupling noises 1 and 2.
Preferably, the first potential is the power supply potential, and the second potential is the ground potential. In this case, the level of coupling noises 1 and 2 that increases or reduces the potential of the signal transfer line higher than the power supply potential or lower than the ground potential can be reduced.
Preferably, the first potential is a potential higher than the power supply potential by the threshold voltage of the diode element, and the second potential is a potential lower than the ground potential by the threshold voltage of the diode element. In this case, the influence of coupling noises 3 and 4 can be reduced since the amplitude voltage of the signal transfer line is increased. Therefore, the margin in detecting the signal level of the signal transfer line can be increased.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.